The present invention relates to an improved process for the preparation of ethanol by the hydrocarbonylation of methanol in the presence of a cobalt-based catalyst.
Ethanol, which is a very valuable industrial product, has conventionally been prepared by the fermentation of various natural substances or by the direct or indirect hydration of ethylene. Numerous processes of industrial synthesis have been developed which use charges of ethylene, this being a petroleum derivative. However, a growing need for processes for the synthesis of heavy chemical products starting from raw materials which do not originate from petroleum has been observed for some years. It is for this reason that it is possible to see an increasingly active interest in the synthesis of chemical products from synthesis gas, i.e., a mixture of carbon monoxide and hydrogen.
In this context, methanol, which can be produced by reacting carbon monoxide with hydrogen and which, in turn, can be reacted with synthesis gas in the presence of cobalt in order to form ethanol, has a very particular importance.
The reaction of methanol with synthesis gas in order to form ethanol, which reaction is still referred to as the homologisation of methanol, has formed and continues to form the subject of much research.
Thus, I. Wender et al. ("Science," Volume 113, page 206, 1951) have shown that methanol reacts with an equimolar mixture of carbon monoxide and hydrogen at 185.degree. C., under a pressure of 360 atmospheres, in the presence of dicobalt octacarbonyl. Under these conditions, a mixture of various products containing ethanol is obtained with a mediocre selectivity. The advantage of this technique has remained purely academic, the hourly productivity of such a catalyst being absurdly low.
Other authors (compare French Pat. No. 1,323,453) have been able substantially to improve the productivity in respect to ethanol by carrying out this reaction at 400 bars and at about 200.degree. C., in the simultaneous presence of cobalt acetate and iodine, the molar ratio CO/H.sub.2 being equal to 0.5.
Subsequently, the same authors further increased this productivity considerably by carrying out the homologisation reaction under the conditions referred to above, with the addition of a very low proportion of a ruthenium halide to the catalyst system based on cobalt acetate and iodine (compare U.S. Pat. No. 3,285,948). In fact, the best results are obtained with about 0.05 to 0.12 gram atom of ruthenium per gram atom of cobalt and correspond to productivities of the order of 350 to 400 g. of ethanol per hour and per liter of reaction medium, and of the order of 200 g. of ethanol per hour and per gram of cobalt (compare Examples Nos. 4, 7, and 12 of the above-mentioned U.S. Patent).
Nevertheless, the possible industrial exploitation of such a process is jeopardized by the elevated pressure required to achieve acceptable hourly productivities.
It has now been found, totally unexpectedly, that it is possible to homologise methanol, under a total pressure of less than 400 bars, with an acceptable hourly productivity in respect to ethanol, in the presence of a cobalt-based catalyst.
It is, therefore, an object of the present invention to provide a novel process for the homologisation of methanol to produce ethanol in commerically practical yields.
It is also an object of the present invention to provide a process for producing ethanol from methanol by homologisation which employs practical pressures.
Other objects will be apparent to those skilled in the art from the present description.